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H Biessmann

Publications and source records attributed to H Biessmann.

At least 37 records · Page 2Linked to original sources
PubMed1994

Telomeric repeat sequences.

Chromosomes not only carry transcribed genes and their regulatory DNA sequences, but also contain regions that are required for the stability and maintenance of the chromosome as a unit. These include centromeres, telomeres and origins of replication. It is clear for replication origins and centromeres that the positions of these chromosomal organelles are determined by sites of the appropriate DNA sequences, but also that functional performance requires one or more contributing proteins. Telomeres are also structurally complex, with one or more DNA components, including simple telomeric repeats and more complex telomere-associated sequences, as well as one or more specific proteins that recognize these sequences. Accumulating evidence suggests that the simple telomeric repeats are required in most, but not all species, although they are not sufficient to determine the chromosomal position of a telomere.

Animals↗
PubMed1993

The genomic organization of HeT-A retroposons in Drosophila melanogaster.

Members of the Drosophila HeT-A family of transposable elements are LINE-like retroposons that are found at telomeres and in centric heterochromatin. We recently characterized an active HeT-A element that had transposed to a broken chromosome end fewer than nine generations before it was isolated. The sequence arrangement of this element, called 9D4, most likely represents the organization of an actively transposing member of the HeT-A family. Here we assess the degree of divergence among members of the HeT-A family and test a model of telomere length maintenance based on HeT-A transposition. The region containing the single open reading frame of this element appears to be more highly conserved than the non-coding regions. The HeT-A element has been implicated in the Drosophila telomere elongation process, because frequent transpositions to chromosome ends are sufficient to counter-balance nucleotide loss due to incomplete DNA replication. The proposed elongation model and the hypothetical mechanism of HeT-A transposition predict a predominant orientation of HeT-A elements with their oligo (A) tails facing proximally at chromosome ends, as well as the existence of irregular tandem arrays of HeT-A elements at chromosome ends resulting from transposition of new HeT-A elements onto chromosome ends with existing elements. Twenty-nine different HeT-A fragments were isolated from directional libraries that were enriched in terminal DNA fragments. Sequence analyses of these fragments and comparisons with the organization of the HeT-A element, 9D4, fit these two predictions and support the model of Drosophila telomere elongation by transposition of HeT-A elements.

Animals↗
PubMed1992

Activation of maternal centrosomes in unfertilized sea urchin eggs.

Centrosomes are undetectable in unfertilized sea urchin eggs, and normally the sperm introduces the cell's microtubule-organizing center (MTOC) at fertilization. However, artificial activation or parthenogenesis triggers microtubule assembly in the unfertilized egg, and this study explores the reappearance and behavior of the maternal centrosome. During activation with A23187 or ammonia, microtubules appear first at the cortex; centrosomal antigen is detected diffusely throughout the entire cytoplasm. Later, the centrosome becomes more distinct and organizes a radial microtubule shell, and eventually a compact centrosome at the egg center organizes a monaster. In these activated eggs, centrosomes undergo cycles of compaction and decompaction in synchrony with the chromatin, which also undergoes cycles of condensation and decondensation. Parthenogenetic activation with heavy water (50% D2O) or the microtubule-stabilizing drug taxol (10 microM) induces numerous centrosomal foci in the unfertilized sea urchin egg. Within 15 min after incubation in D2O, numerous fine centrosomal foci are detected, and they organize a connected network of numerous asters which fill the entire egg. Taxol induces over 100 centrosomal foci by 15 min after treatment, which organize a corresponding number of asters. The centrosomal material in either D2O- or taxol-treated eggs aggregates with time to form fewer but denser foci, resulting in fewer and larger asters. Fertilization of eggs pretreated with either D2O or taxol shows that the paternal centrosome is dominant over the maternal centrosome. The centrosomal material gradually becomes associated with the enlarged sperm aster. These experiments demonstrate that maternal centrosomal material is present in the unfertilized egg, likely as dispersed undetectable material, which can be activated without paternal contributions. At fertilization, paternal centrosomes become dominant over the maternal centrosomal material.

Ammonia↗
PubMed1992

Frequent transpositions of Drosophila melanogaster HeT-A transposable elements to receding chromosome ends.

HeT-A elements are a new family of transposable elements in Drosophila that are found exclusively in telomeric regions and in the pericentric heterochromatin. Transposition of these elements onto broken chromosome ends has been implicated in chromosome healing. To monitor the fate of HeT-A elements that had attached to broken ends of the X chromosome, we examined individual X chromosomes from a defined population over a period of 17 generations. The ends of the X chromosomes with new HeT-A additions receded at the same rate as the broken ends before the HeT-A elements attached. In addition, some chromosomes, approximately 1% per generation, had acquired new HeT-A sequences of an average of 6 kb at their ends with oligo(A) tails at the junctions. Thus, the rate of addition of new material per generation matches the observed rate of terminal loss (70-75 bp) caused by incomplete replication at the end of the DNA molecule. One such recently transposed HeT-A element which is at least 12 kb in length has been examined in detail. It contains a single open reading frame of 2.8 kb which codes for a gag-like protein.

Amino Acid Sequence↗
PubMed1992

HeT-A, a transposable element specifically involved in "healing" broken chromosome ends in Drosophila melanogaster.

Eight terminally deleted Drosophila melanogaster chromosomes have now been found to be "healed." In each case, the healed chromosome end had acquired sequence from the HeT DNA family, a complex family of repeated sequences found only in telomeric and pericentric heterochromatin. The sequences were apparently added by transposition events involving no sequence homology. We now report that the sequences transposed in healing these chromosomes identify a novel transposable element, HeT-A, which makes up a subset of the HeT DNA family. Addition of HeT-A elements to broken chromosome ends appears to be polar. The proximal junction between each element and the broken chromosome end is an oligo(A) tract beginning 54 nucleotides downstream from a conserved AATAAA sequence on the strand running 5' to 3' from the chromosome end. The distal (telomeric) ends of HeT-A elements are variably truncated; however, we have not yet been able to determine the extreme distal sequence of a complete element. Our analysis covers approximately 2,600 nucleotides of the HeT-A element, beginning with the oligo(A) tract at one end. Sequence homology is strong (greater than 75% between all elements studied). Sequence may be conserved for DNA structure rather than for protein coding; even the most recently transposed HeT-A elements lack significant open reading frames in the region studied. Instead, the elements exhibit conserved short-range sequence repeats and periodic long-range variation in base composition. These conserved features suggest that HeT-A elements, although transposable elements, may have a structural role in telomere organization or maintenance.

Animals↗
PubMed1991

The fat tumor suppressor gene in Drosophila encodes a novel member of the cadherin gene superfamily.

Recessive lethal mutations in the fat locus of Drosophila cause hyperplastic, tumor-like overgrowth of larval imaginal discs, defects in differentiation and morphogenesis, and death during the pupal stage. Clones of mutant cells induced by mitotic recombination demonstrate that the overgrowth phenotype is cell autonomous. Here we show that the fat locus encodes a novel member of the cadherin gene superfamily: an enormous transmembrane protein of over 5000 amino acids with a putative signal sequence, 34 tandem cadherin domains, four EGF-like repeats, a transmembrane domain, and a novel cytoplasmic domain. Two recessive lethal alleles contain alterations in the fat coding sequence, and the dominant fat allele, Gull, contains an insertion of a transposable element in the 33rd cadherin domain. Thus, this novel member of the cadherin gene superfamily functions as a tumor suppressor gene and is required for correct morphogenesis.

Alleles↗
PubMed1991

Temporal and spatial expression of the yellow gene in correlation with cuticle formation and dopa decarboxylase activity in Drosophila development.

The yellow (y) gene of Drosophila is required for the formation of black melanin and its deposition in the cuticle. We have studied by immunohistochemical methods the temporal and spatial distribution of the protein product of the y gene during embryonic and pupal development and have correlated its expression with events of cuticle synthesis by the epidermal cells and with cuticle sclerotization. Except for expression in early embryos, the y protein is only found in the epidermal cells and may be secreted into the cuticle as it is being deposited. The amount of y protein in various regions of the embryo and pupa correlates directly with the intensity of melanization over any section of the epidermis. Expression of the y gene begins in the epidermal cells at 48 hr after pupariation and is well correlated with the beginning deposition of the adult cuticle. At this stage the adult cuticle is unsclerotized and unpigmented and dopa decarboxylase levels, a key enzyme in catecholamine metabolism which provides the crosslinking agents as well as the precursors for melanin, is low. As a separate event 26 hr after the onset of y gene expression, the first melanin deposition occurs in the head bristles and pigmentation continues in an anterior to posterior progression until eclosion. This melanization wave is correlated with elevated dopa decarboxylase activity. Crosslinking of the adult cuticle also occurs in a similar anterior to posterior progression at about the same time. We have shown by imaginal disc transplantation that timing of cuticle sclerotization depends on the position of the tissue along the anterior-posterior axis and that it is not an inherent feature of the discs themselves. We suggest that actual melanization and sclerotization of the cuticle by crosslinking are initiated at this time in pupal development by the availability of the catecholamine substrates which diffuse into the cuticle. Intensity of melanization and position of melanin pigment is determined by the presence or absence of the y protein in the cuticle, thus converting the y protein prepattern into the melanization pattern.

Animals↗
PubMed1990

Addition of telomere-associated HeT DNA sequences "heals" broken chromosome ends in Drosophila.

Stocks of D. melanogaster X chromosomes carrying terminal deletions (RT chromosomes) have been maintained for several years. Some of the chromosomes are slowly losing DNA from the broken ends (as expected if replication is incomplete) and show no telomere-associated DNA added to the receding ends. Two stocks carry chromosomes that have become "healed" and are no longer losing DNA. In both stocks the broken chromosome end has acquired a segment of HeT DNA, a family of complex repeats found only at telomeres and in pericentric heterochromatin. Although the HeT family is complex, the HeT sequence joined to the broken chromosome end is the same in both stocks. In contrast, the two chromosomes are broken in different places and have no detectable sequence similarity at the junction with the new DNA. Sequence analysis suggests that the new telomere sequences have been added by a specific mechanism that does not involve homologous recombination.

Animals↗
PubMed1990

Heat shock causes the collapse of the intermediate filament cytoskeleton in Drosophila embryos.

Heat shock has a dramatic effect on the organization of the cytoplasm, causing the intermediate filament cytoskeleton to aggregate at the nucleus. This has previously been shown in cultured Drosophila and mammalian cells. In this paper we analyze the heat lability of the intermediate filament cytoskeleton in early Drosophila embryos by indirect immunofluorescence. At all stages of embryogenesis tested, the intermediate filament cytoskeleton, which is maternally provided, is severely disturbed by 30 min heat shock at 37 degrees C. After the nuclei have migrated to the subcortical cytoplasm, it collapses around them. Nuclei in all heat-shocked embryos are considerably enlarged and become displaced. Embryos before cellular blastoderm stage, in which heat shock protein synthesis is not inducible, are irreversibly arrested in development by heat shock. Embryos at or after cellular blastoderm, which do synthesize heat shock proteins in response to stress, are also immediately arrested in development but continue development when returned to 25 degrees C. We discuss the possibility that cytoplasmic events such as the intermediate filament cytoskeleton rearrangement may be involved in heat shock-mediated phenocopy induction.

Animals↗
PubMed1990

Chromosome ends in Drosophila without telomeric DNA sequences.

We have recovered terminal chromosome deletions of the X chromosome of Drosophila [Df(1)RT; RT = receding tips] that break in various positions of the yellow gene (y) region and delete all distal DNA sequences. Terminal DNA fragments are heterogeneous in length. Molecular cloning and sequencing of the terminal DNA fragments revealed that the broken ends of the deleted chromosomes do not carry any telomeric DNA sequences, yet the broken chromatids do not fuse to one another. Moreover, we confirmed by sequence analysis of 49 independently cloned terminal DNA fragments from two RT lines collected at different times that they lose DNA sequences from their distal ends at a rate of 70-75 base pairs per fly generation. We calculate that the rate of loss from these ends is consistent with the removal of an octanucleotide RNA primer at each round of DNA replication in the germ line.

Animals↗
PubMed1989

Overexpression of a 123-kDa anion transport inhibitor binding protein and two cytoskeleton proteins in Drosophila Kc cell variants resistant to disulfonic stilbenes.

Drugs of the disulfonic stilbene class, which inhibit anion transport in the cell membrane in many cell types, have been found to inhibit anion transport and cell growth in Drosophila Kc cells. Cell variants selected by a stepwise selection protocol for the ability to grow in the presence of the disulfonic stilbenes are severalfold resistant to growth inhibition by the drugs. Both the resistant populations and a cloned cell line show dramatic overexpression of three polypeptides. The most highly overproduced protein is a 123-kDa plasma membrane protein which binds the reversible anion transport inhibitor, flufenamic acid, in a protection biotinylation experiment. The 123-kDa putative anion transport protein copurifies with, and immunologically cross-reacts with, two detergent-insoluble cytoskeleton proteins of 46- and 62-kDa molecular weight, which are each overexpressed more than 8-fold in the variants. Resistance to growth inhibition by the disulfonic stilbenes and amplified expression of the 123-, 62-, and 46-kDa proteins are simultaneously lost over a period of 30 weeks in the absence of selective conditions, suggesting that the function of the overproduced polypeptides is related to growth control in Drosophila cells.

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗
PubMed1988

Microtubules are required for centrosome expansion and positioning while microfilaments are required for centrosome separation in sea urchin eggs during fertilization and mitosis.

Centrosomes undergo cell cycle-dependent changes in shape and separations, changes that govern the organization of the cytoskeleton. The cytoskeleton is largely organized by the centrosome; however, this investigation explores the importance of cytoskeletal elements in directing centrosome shape. Since the sea urchin egg during fertilization and mitosis displays dramatic and synchronous changes in centrosome shape, the effects of cytoskeletal inhibitors on centrosome compaction, expansion, and separation were explored by the use of anticentrosome immunofluorescence microscopy. Centrosome expansion and separation was studied during two phases: the transition after sperm incorporation, when the compact sperm centrosome enlarges and the sperm aster develops, and from prometaphase to telophase, when the compact spindle poles enlarge. Compaction was investigated when the dispersed centrosome at interphase condenses into the two spindle poles at prometaphase. Although centrosome expansion and separation typically occur concurrently, beta-mercaptoethanol results in centrosome separation independent of expansion. Microtubule inhibitors prevent centrosome expansion and separation, and expanded centrosomes collapse. Since pronuclear union is arrested by microtubule inhibitors, this treatment also affords the opportunity to explore the relative attractiveness of the male and female pronuclei for these centrosomal antigens. Both pronuclei acquire centrosomal material; though only the male centrosome is capable of organizing a functional bipolar mitotic apparatus at first division, the female centrosome nucleates a monaster. Microfilament inhibition (cytochalasin D) prevents centrosome separation but not expansion or compaction. These results demonstrate that as the centrosome shapes the cytoskeleton, the cytoskeleton alters centrosome shape.

Actin Cytoskeleton↗
PubMed1988

Progressive loss of DNA sequences from terminal chromosome deficiencies in Drosophila melanogaster.

Terminal deficiencies at the tip of the X chromosome can be induced at a high frequency (0.2-0.3%) by irradiating Drosophila females carrying a homozygous mutator (mu-2) with low doses of X-rays. These terminal deficiencies are unstable, since over a period of 3 1/2 years DNA sequences were lost from their distal ends at a rate of 75 bp per generation, presumably due to the absence of a complete wild-type telomeric structure. Breakpoints of these deletions in the 5' upstream regulatory region of the yellow gene, giving rise to a mosaic cuticle pigmentation pattern typical of the y2 type, were used to define the location of tissue-specific cis-acting regulatory elements that are required for body, wing or bristle pigmentation.

Animals↗
PubMed1987

A non-filamentous configuration of intermediate-sized filament proteins in Drosophila Kc tissue culture cells.

Using monoclonal antibodies against the major intermediate filament (10 nm) cytoskeletal proteins of Drosophila tissue culture cells, we showed by indirect immunofluorescence and immuno-electron microscopy that this cytoskeletal material also occurs in a non-filamentous configuration. Patches of fine granular material are detected in the cytoplasm of Kc cells but are absent in another Drosophila cell line (Schneider, line 2). These patches are surrounded by membranes with bound ribosomes, resembling endoplasmic reticulum, and are found throughout the cytoplasm. We suggest that these aggregates are caused by overproduction of intermediate filament material in the Kc cell line.

Animals↗
PubMed1987

Centrosome detection in sea urchin eggs with a monoclonal antibody against Drosophila intermediate filament proteins: characterization of stages of the division cycle of centrosomes.

A mouse monoclonal antibody generated against Drosophila intermediate filament proteins (designated Ah6/5/9 and referred to herein as Ah6) is found to cross-react specifically with centrosomes in sea urchin eggs and with a 68-kDa antigen in eggs and isolated mitotic apparatus. When preparations stained with Ah6 are counterstained with a human autoimmune serum whose anti-centrosome activity has been established, the immunofluorescence images superimpose exactly. A more severe test of the specificity of the antibody demands that it display all of the stages of the centrosome cycle in the cell cycle: the flattening and spreading of the compact centrosomes followed by their division and the establishment of two compact poles. The test was made by an experimental design that uses a period of exposure of the eggs to 2-mercaptoethanol. This treatment allows observation of the stages of the centrosome cycle--separation, division, and bipolarization--while the chromosomes are arrested in metaphase. Mitosis is arrested in the presence of 0.1 M 2-mercaptoethanol. Chromosomes remain in a metaphase configuration while the centrosomes divide, producing four poles perpendicular to the original spindle axis. Microtubules are still present in the mitotic apparatus, as indicated by immunofluorescence and transmission electron microscopy. When 2-mercaptoethanol is removed, the chromosomes reorient to the poles of a tetrapolar (sometimes tripolar) mitotic apparatus. During the following cycle, the blastomeres form a monopolar mitotic apparatus. The observations of the centrosome cycle with the Ah6 antibody display very clearly all the stages that have been seen or deduced from work with other probes. The 68-kDa antigen that reacts with the Ah6 monoclonal antibody to Drosophila intermediate filament proteins must be a constant component of sea urchin centrosomes because it is present at all stages of the centrosome cycle.

Animals↗
PubMed1986

Small heat shock proteins of Drosophila associate with the cytoskeleton.

Fractionation of heat-shocked Drosophila melanogaster Kc cells reveals that both the small heat shock proteins (hsp28, -26, -23, and -22) and vimentin-like intermediate filament proteins (IFPs) are abundantly represented in the nuclear fraction. Cofractionation of the IFPs with nuclei is due to the collapse of the IFP network against the nucleus upon heat shock, raising the possibility that cofractionation of the small hsps is by a similar mechanism. Indirect immunofluorescence supports this possibility. In salivary glands, both the hsps and the IFPs are cytoplasmic after mild-to-moderate heat shocks and only enter the nucleus upon severe--indeed, lethal--shocks. Double-label experiments with Schneider line 2 cells show that the IFPs and small hsps colocalize to the same perinuclear aggregates in 70% of the cells examined. Thus, the small hsps are associated with the cytoskeleton rather than with nuclear structures.

Animals↗